How to Install Duct Work

Most heating and air conditioning systems are forced air systems. The system blows air through ducts to the living spaces, heating and cooling a room as required. Duct work includes a supply line that sends fresh air into the rooms and a return line that removes stale air from the rooms. Installing the duct work takes planning and patience. Each pipe must be meticulously placed to ensure the proper air flow in the home.

Select ducting pipe size according to the cubic feet per minute (cfm) needed for the room.  Multiplying the room length by the room width equals the square footage.  One cfm of air is need for 1 to 1.25 square feet.  A 120 square foot room will need between 96 to 120 cfm of air.  A six inch diameter pipe will provide adequate air flow.

Install the starting collar at the side of the plenum.  Use the starting collar to mark an opening.  Use a sharp tool to cut the opening.  Insert the collar into the opening.  Secure the starting collar with sheet metal screws.  Seal it with mastic or duct sealant.

Use measuring tape to measure space between the air conditioning system and the room.  Determine the length of ducting required for the project. Attach ducting to the starter collar.  Join additional ducting or pipes, as needed until the ducting reaches the room.  Attach additional ducting with sheet metal screws.  Seal with mastic.

Install a floor diffuser or supply register in the floor.  Cut hole into the floor the size of an air vent.  Connect the register to the floor with nails.  Connect the branch line to the register with sheet metal screws.  Seal with mastic.

Create a return.  Connect ducting to a return branch.  Install a point of return in the room that is as far away from the air supply line as possible.  If the supply line vent is in the floor, the return vent should be in the ceiling. 

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